SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 833 
Whether this can be assumed to hold generally is, of course, not established, but 
may be regarded as probable. 
A good example is represented in figs. 6-8. As the general low-power view 
(fig. 6) shows, the plane of section has passed tangentially to a stem of Rhynia 
Gwynne-Vaugliani. A portion of the stem bears two hemispherical projections 
cut in oblique tangential section and in part seen from the outer surface. Con- 
tinuing the line of the stem, another hemispherical projection that was evidently 
borne on the same surface has been shaved off by the section and is viewed directly 
from above. The two portions are more highly magnified in figs. 7 and 8. A 
stoma ( s .) is seen clearly in relation to the lower of the attached projections in fig. 7, 
while the position of the stoma is indicated by a dark patch on the surface of the 
other projection. The stoma ( s .) is 'Seen quite clearly on the isolated projection in 
fig. 8. A number of examples similar to this have been observed, and in them also 
the position of the stoma was near one end of the oval projection. Whether this 
was the end directed towards the base or apex of the plant is uncertain. The 
additional example in fig. 9 shows the stoma (,s.) at one end of a small projection, 
apparently in an early stage of development. 
In the light of these specimens it is clear that the hemispherical projections 
cannot be regarded as part of the primary construction of the plant as at first 
developed. 
Many of the hemispherical projections did not undergo further development or 
change. What appears to have been an exudation, in which fungi often grew, 
sometimes formed to the outside of the projection as the stems lay in the matrix. 
In other cases the projections were the seat of further developments. A single 
specimen has been seen ill which a projection, prolonged vertically from the surface, 
resembles an emergence (PI. Ill, fig. 10). Sometimes their superficial cells grew 
out as rhizoids (Part I, figs. 52-54). At other times growth resulted in the 
development of lateral, adventitious branches; these in some cases remained small, 
and may have fallen off and served as a means of vegetative reproduction ; often, 
however, they were larger and more strongly attached, though their vascular system 
was separate from that of the stem bearing them (Part I, figs. 55-60). 
Comparisons of the peculiar hemispherical projections on the stems of Rhynia 
Gwynne-Vaugliani are possible both with normal and pathological developments 
in recent plants. 
They show certain resemblances to lenticels which, when formed in relation to 
the original surface of a stem, usually develop below the stomata. Nothing in the 
details of structure of the hemispherical projections of Rhynia indicates, however, 
that they were related to normal gaseous exchange. This comparison is thus not a 
very close one. 
A more suggestive comparison is with certain intumescences that form on the 
stems and leaves of various plants, either as a result of the excessive moisture of 
